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  Java SE基础篇(一)
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      <a href="/2020/07/01/Java-SE%E5%9F%BA%E7%A1%80%E7%AF%87-%E4%B8%80/" class="article-date">
  <time datetime="2020-07-01T13:50:02.000Z" itemprop="datePublished">2020-07-01</time>
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      <h2 id="一、计算机存储单元"><a href="#一、计算机存储单元" class="headerlink" title="一、计算机存储单元"></a>一、计算机存储单元</h2><p>计算机存储设备的最小信息叫“<strong>位(bit)</strong>”,通常用“b”表示，而计算机中最小的存储单元叫“<strong>字节（byte）</strong>”,常用“B”表示，字节是由连续的8位组成。</p>
<h2 id="二、数据类型"><a href="#二、数据类型" class="headerlink" title="二、数据类型"></a>二、数据类型</h2><p>java语言是强类型语言，对于每一种数据都给出了明确的数据类型，不同的数据类型也分配了不同的内存空间<br><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/20200701.jpg" alt=""></p>
<a id="more"></a>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-01_20-08-23.jpg" alt=""></p>
<h2 id="三、常量"><a href="#三、常量" class="headerlink" title="三、常量"></a>三、常量</h2><p>常量是指在程序运行过程中其值不可以发生改变的量</p>
<h3 id="常量分类"><a href="#常量分类" class="headerlink" title="常量分类"></a>常量分类</h3><p>字符串常量、整数常量、小数常量、字符常量、布尔常量、空常量（null）</p>
<h2 id="四、变量"><a href="#四、变量" class="headerlink" title="四、变量"></a>四、变量</h2><p>变量是指在程运行过程中其值可以发生改变的量</p>
<h3 id="变量定义"><a href="#变量定义" class="headerlink" title="变量定义"></a>变量定义</h3><p><strong>变量类型  变量名 = 变量值;</strong></p>
<p>例如： int a=5;</p>
<h3 id="变量使用注意事项"><a href="#变量使用注意事项" class="headerlink" title="变量使用注意事项"></a>变量使用注意事项</h3><ul>
<li><p>若定义变量时未给变量赋值则无法使用</p>
</li>
<li><p>如果你想要一个长整型（long）那么就要在后面加上<strong>L</strong>加以区分,否则还是默认的int类型</p>
<p>如：long c=10000000000L;</p>
</li>
<li><p>同理float类型也需要加<strong>F</strong>或<strong>f</strong>加以区分</p>
</li>
</ul>
<p>如：float d=13.14F;</p>
<h2 id="五、标识符"><a href="#五、标识符" class="headerlink" title="五、标识符"></a>五、标识符</h2><p>标识符指给类，方法、变量等起名字的符号。</p>
<h3 id="规则"><a href="#规则" class="headerlink" title="规则"></a>规则</h3><ul>
<li>由 <strong>数字</strong>、<strong>字母</strong>、<strong>下划线</strong>、<strong>$</strong> 组成</li>
<li>不能以<strong>数字</strong>开头</li>
<li>不能是<strong>关键字</strong></li>
<li><strong>区分大小写</strong></li>
</ul>
<p>案例（<strong>class</strong>不符合规则，但<strong>Class</strong>符合标识符规则）</p>
<h3 id="常见的命名规则"><a href="#常见的命名规则" class="headerlink" title="常见的命名规则"></a>常见的命名规则</h3><p><strong>小驼峰</strong></p>
<p>针对方法、变量</p>
<p>如：<a href="#">handle</a>、<a href="#">firstName</a></p>
<p><strong>大驼峰</strong></p>
<p>针对类</p>
<p>如：<a href="#">Student</a>、<a href="#">SecondRecord</a></p>
<h2 id="六、类型转换"><a href="#六、类型转换" class="headerlink" title="六、类型转换"></a>六、类型转换</h2><h3 id="自动类型转换"><a href="#自动类型转换" class="headerlink" title="自动类型转换"></a>自动类型转换</h3><p><strong>把一个表示数据范围小的数值或者变量赋值给另一个表示数据范围大的变量，其中两种类型是彼此兼容的</strong></p>
<ul>
<li>大的装小的</li>
</ul>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-01_21-04-11.jpg" alt=""></p>
<p><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-01_21-02-58.jpg" alt=""></p>
<h3 id="强制类型装换"><a href="#强制类型装换" class="headerlink" title="强制类型装换"></a>强制类型装换</h3><p><strong>把一个表示范围大的值或变量赋给一个表示数据小的变量</strong></p>
<ul>
<li>小的装大的</li>
</ul>
<p>存在精度损失和强制转换过程中发生数据溢出的风险<br><img src="https://yolin121.oss-cn-beijing.aliyuncs.com/blogimg/Snipaste_2020-07-01_21-15-53.jpg" alt=""></p>
<h3 id="类型提升"><a href="#类型提升" class="headerlink" title="类型提升"></a>类型提升</h3><p><strong>类型提升是指在多种不同数据类型的表达式中，类型会自动向范围表示大的值的数据类型提升</strong>。</p>
<p>好比一个int类型的变量与long类型的变量相乘的结果为long类型</p>
<ul>
<li>如果两个操作数其中有一个是double类型，另一个操作就会转换为double类型。</li>
<li>否则，如果其中一个操作数是float类型，另一个将会转换为float类型。</li>
<li>否则，如果其中一个操作数是long类型，另一个会转换为long类型。</li>
<li>否则，两个操作数都转换为int类型。</li>
</ul>
<h2 id="思维导图"><a href="#思维导图" class="headerlink" title="思维导图"></a>思维导图</h2><p>最后附上整理的导图，内容会不断更新，加油ヾ(◍°∇°◍)ﾉﾞ</p>
<p><a href="http://www.yolin.xyz/web_test/mind.svg" target="_blank" rel="noopener">Java EE思维导图</a></p>

      
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